I retired as an industrial design engineer and used to design a lot of pre engineered steel buildings and my freight elevators but I was never licensed as a PE here in the USA my exploits were mostly overseas. so far as your trusses go as small as your enclosure is, like I said you shouldn't have any problem just buying a few 12 to 16"bar joists long enough to do the job cut the bottom angles then bend them to the shape you require and have a welder weld them back together with a strip of bent flat bar welded underneath something like 3/8 by 4" with the 2 legs being as long as the height of the bar joist. I can draw it for you but can not provide a stamp if you require that you would have to seek out a PE.